Many diseases can be prevented by a healthy diet, but making informed food choices depends on knowledge, access and, of course, money. Ann Ralph reports on the big divide between rich and poor

It's the rich wot gets the pleasure, it's the poor wot gets the blame," goes the old refrain. Unpalatable as it is, the shaming reality at the end of the late 20th century is that there remains a great divide between the health of different social classes. It was spelled out back in 1980 in the report by a research working group chaired by Sir Douglas Black on inequalities in health. Although general health was improving, a clear differential was emerging between social groups in infant mortality from infections, and in adult death rates from chronic disease.

Viewed as a legacy of a defeated Labour administration, the Black report was consigned to Whitehall oblivion. The Thatcher government released a few copies on August bank holiday 1980. What should have been the turning point in addressing the nation's health became a distant milestone forgotten by Tory ministers throughout the Tory years.

Not that their advisers failed to remind them of the reality. Recognition that the high risk factors of heart disease and stroke - high blood pressure, diet, stress, smoking, obesity and physical inactivity - were not just symptoms of poverty but of inequality came from Sir Donald Acheson, government chief medical officer until 1991. In 1995 he expressed concern that while the nation's health was improving, inequalities between social groups were widening.

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The present government has gone full circle to return to the original premise of the Black report. Health ministers Frank Dobson and Tessa Jowell hope to find ways of tackling this health divide, the origins of which are complex. Diet has always been considered a risk factor for health, although the classical diseases of a deficient diet, such as scurvy, gotre and rickets are rare in Britain. Most cancers, except for breast and bowel cancer, are more prevalent in the lower social classes. Last week, a report, Food, Nutrition and the Prevention of Cancer, made recommendations to reduce the risk of many common cancers. These included advice to choose mainly plant-based diets, to eat daily 400-500g of vegetables and fruit and 600-800g cereals, to limit red meat to less than 80g a day and to ensure that fats and oils provide less than 30 per cent of daily energy requirement. Salt intake should be limited to less than 6g a day and alcohol to fewer than two drinks a day for men, and one for women.

In these days of the welfare state, free education, an abundance of cheap supermarket food and a decade of health education messages, we might assume that no one is short of food and everyone knows what they should be eating. But making an informed choice about what to eat depends on knowledge, access and money - requisites that are not readily available to the poor.

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Many people in the lower socio-economic groups are young single parents or the elderly. Surveys reveal that the poor claim to know what they should be eating but find it difficult to do so. Many young people today probably never learned to cook. Reared on processed food, they know little about different cuts of meat, types of fresh fish or how to use vegetables and fruit. Older people may know how to buy and cook for economical dishes such as soups or stews from cheap cuts of meat and root vegetables, but they have difficulties in shopping for food.

A single parent with little money living on a large housing estate is unlikely to have a car to get to the supermarket, which may be several bus rides away. More than a quarter of greengrocers have closed in the last decade. Local shops often stock a limited range of long shelflife goods costing up to 30 per cent more than at supermarkets, while fruit and vegetables are very limited and often not very fresh. Tins and economy-size packs are heavy and difficult to carry. The children will not eat things they do not like, so hard-up parents buy what they will eat, so there is no waste. To cook quickly, the food is probably fried in fat or cheap oil. It may be easier to go to the local chippy. Fruit is not nearly as comforting as chocolate.

Recent research has gone a long way towards exploding myths about food and the poor such as "If they don't eat a healthy diet it's their own fault" or "Healthy food isn't expensive". New definitions of food poverty are emerging. One of the best is: "The inability to acquire or consume an adequate quality or sufficient quantity of food in socially acceptable ways."

The annual household food survey gives details of expenditure on and consumption of food and nutrients by region, family composition, social class and income group. The statistics show that compared with the highest income group A (gross weekly income of the head of household over Pounds 790), low-income groups D and E2 (under Pounds 140 a week) have a less healthy diet. They drink more milk but less of it semi-skimmed, eat more meat and meat products, more fats, sugar, preserves, potatoes and refined cereal products. They eat fewer fresh vegetables and fruit and high-fibre products.

The poorest 10 per cent of the population spend 29 per cent of their disposable income on food, while the richest 10 per cent spend 18 per cent. Contrary to popular myth, the poor spend more efficiently in certain respects. A carrot may be cheaper and healthier than a chocolate bar but it has fewer calories. Mainstream healthy food options are likely to cost an extra 10 per cent, so poor people are buying for calories that are cheap, not for vitamins and nutrients that are more expensive, and tend to come in low-calorie foods.

This results in a lower intake of many vital nutrients (calcium, iron, magnesium, the B vitamin, folate - found in leafy vegetables - other B vitamins and vitamin C) among low-income groups. While their vitamin intake may not be low enough to cause scurvy, there is now evidence that higher levels of certain nutrients play a protective role in many diseases. Vitamins A, C, and E are known as antioxidants and protect from free-radical damage, a natural phenomenon with some beneficial effects but also thought to be responsible for aspects of heart disease, ageing and cancer.

Over the past 15 years our total food consumption has fallen, reflecting an increasingly sedentary lifestyle requiring fewer calories. But as intake declines, it is more difficult to obtain sufficient micronutrients, the essential vitamins and minerals. Our diets need to become richer in these to compensate. Not surprisingly, the well-off have been better able to make this adjustment than the poor, so there has been a growing disparity in the quality of the diet between classes. The consumption of fruit, vegetables, carotene (a form of vitamin A found in carrots and other red, yellow and orange plant foods) and vitamin C has declined in both groups, but for everything except vitamin C, the differences between rich and poor are greater now than 15 years ago.

These differences have consequences that can be seen at all ages. In pregnancy, both lack of adequate nutrition and smoking lead to premature, low birth weight babies. Diets low in folate predispose to shorter pregnancy, low birth weight and defects such as spina bifida. Lack of omega-3 fatty acids present in oily fish contributes to heart disease. A diet low in vegetables and fruit also contributes to heart disease through low anti-oxidant levels. Low intakes of folate increase homocysteine levels in the blood, a risk factor for heart disease, stroke and other circulatory problems. Trans-fatty acids, found in the hydrogenated hard margarines used in cheap bakery products, also contribute to thrombosis and low birth weights.

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Obesity, particularly of the abdomen, is twice as prevalent in women in the lower social class groups in Britain. It has been linked to poor foetal growth conditions and to long-term stress and is also associated with diabetes, heart disease, some cancers, breathlessness, menstrual disturbances, pregnancy complications, back pain, arthritis, skin disorders and varicose veins. The causes of obesity are complex and probably have a genetic component, but include lack of exercise and a high-fat, energy-dense diet.

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Over 13 million people and one-third of children live in households with incomes of less than Pounds 120 a week. Poor diet affects the health of the socially disadvantaged from cradle to grave, but the potential for improved health through a better diet is enormous. A low-quality diet, lack of exercise, and smoking are a lethal triad, leading to an inter-generational spiral of ill health and handicap.

The British hate being told what to eat, distrust most official advice and have their own theories about food. The box below gives some totally unofficial advice, which the poor are unable to follow.

Ann Ralph is scientific assistant to Philip James, director of the Rowett Research Institute, Aberdeen.

Unofficial tips for a healthy diet

* Eat starchy basic foods - bread, potatoes, rice, pasta -with every meal

* Eat at least five portions a day of vegetables and fruit. Include green leaves for folate, citrus for vitamin C, and yellow/orange for carotene

* Eat oily fish - herrings, sardines, mackerel, etc - twice a week

* Use olive oil or quality vegetable oils for cooking or salad dressings

* Use butter or margarine sparingly

* Choose lean cuts of meat or remove fat but eat meat in moderation (two to three times a week) and cook carefully

* Eat meat products sparingly (once a week) and choose low-fat varieties

* Drink semi-skimmed milk and use lower fat cheeses

* Drink water when you are thirsty - drink it with your children

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* Enjoy a glass of wine or beer with your meal

* Limit to once or twice a week: chips, crisps, salted or smoked foods, sweets, cakes, biscuits, cream, ice cream, sweet soft and fizzy drinks